The present invention relates to a transmission line type component which is an electronic component suitable as a high frequency decoupling device (a decoupling component, i.e., a so called decoupler) mainly in a semiconductor switching circuit and is mounted as a power supply line of a digital printed circuit board or semiconductor package having high speed, high frequency circuit elements.
As is well known, printed circuit boards having high speed, high frequency circuit elements represented by, e.g., an LSI (Large Scale Integrated) circuit conventionally have such a problem that electromagnetic noise generated from the circuit board induces electromagnetic interference or EMI (Electromagnetic Interference), and this causes an operation error in the electronic device that has the board or in another electronic device.
An especially large part of generated electromagnetic noise is electromagnetic noise called common mode noise which is caused by a high frequency source generated on the basis of a large land surface or ground surface called a common mode and serving as a reference potential. Common mode noise may be generated as a result of many possible reasons. In addition, the mechanism that generates common mode noise is complex, and it is difficult to take an effective measure at a portion near the generation source. Normally, a leakage preventing measure or a radiation preventing measure is taken for a cable that serves as a main propagation line or radiation antenna of common mode noise.
On the other hand, recent studies reveal that one of the major causes of common mode noise in a high speed digital circuit is the high frequency power supply current of a high speed, high frequency circuit element mounted on a printed circuit board. Techniques have also been developed to obtain an effect for suppressing EMI caused by the high frequency power supply current of such a high speed, high frequency circuit element. Examples of known techniques are a multilayered printed board disclosed in Japanese Patent Laid Open No. 9 139573 and a printed wiring board disclosed in Japanese Patent Laid Open No. 11 40915.
In these techniques, DC power supply for a high speed, high frequency circuit element mounted on a printed circuit board is accomplished by providing a line which has an inductor with a high impedance in a high frequency mode inserted midway or a line (to be referred to as a decoupling inductor hereinafter) having a high characteristic impedance and a magnetic body inserted midway, and accordingly, a capacitor (to be referred to as a bypass capacitor hereinafter) is connected between the power supply line and the ground line of the high speed, high frequency circuit element to smoothly execute high speed, high frequency operation in the high speed, high frequency circuit element, and meanwhile, prevent a high frequency power supply current, which is generated in accordance with the operation, from diffusing to the entire circuit board.
FIG. 10 shows the basic arrangement of a conventional decoupling circuit having an EMI suppressing effect (an equivalent circuit representing the technical principle of the EMI suppressing effect disclosed in Japanese Patent Laid Open No. 9 139573).
In this decoupling circuit, in an LSI 6 whose input and output sides are connected to a DC power supply 10 respectively through a power supply line 8 and ground line 9, a decoupling inductor 22 made of a coil L is inserted to the power supply line 8. In addition, a bypass capacitor 19 having an electrostatic capacitance C is inserted between the power supply line 8 and the ground line 9, thereby constituting a power supply circuit.
The above described measure against a high frequency power supply current, including such a decoupling circuit (power supply circuit), is appropriate from the technical viewpoint. Practically, however, a high frequency power supply current that is substantially generated in accordance with the high speed, high frequency operation of the high speed, high frequency circuit element is not taken into consideration (generation of a high frequency power supply current or a technique for suppressing it is not disclosed at all). To practice the measure, the parameters of the decoupling inductor and bypass capacitor must be designed for each LSI. Furthermore, a commercially available capacitor can hardly be applied because commercially available capacitors do not have characteristics which can adequately accommodate an increase in speed of an LSI.
On the other hand, for such power supply circuits, research and development of techniques that can be used for the time being as measures against a high frequency power supply current and can relatively easily be put into practice in place of the above described decoupling circuit (power supply circuit) are progressing because of the necessity for increasing the operation speed of digital circuits, although there are many problems. An example of a known technique that is supposed to be associated with such a technique is a multilayered printed circuit board incorporating a high-k dielectric and having a DC power supply line, which is proposed in Japanese Patent Application No. 11 229525.
In this technique, a DC power supply whose internal impedance has a sufficiently small value over a wide frequency band, which is an ideal power supply form for a high speed, high frequency circuit element such as an LSI mounted on a printed circuit board, is arranged for each high speed, high frequency circuit element so that a high frequency power supply current generated in accordance with the high speed, high frequency operation of the high speed, high frequency circuit element can flow smoothly, and as a consequence, the distortion of signal waveform can be suppressed. In addition, the voltage is stabilized by sharing the DC power supply, thereby eliminating interference between the high speed, high frequency circuit elements.
FIG. 11 is a plan view showing the arrangement of main part of the conventional multilayered printed circuit board incorporating a high-k dielectric and having a DC power supply line, which has an EMI suppressing effect (a printed circuit board proposed in Japanese Patent Application No. 11 229525).
In this multilayered printed circuit board incorporating a high-k dielectric, seven LSIs 6h, 6i, 6j, 6k, 6l, 6m, and 6n are connected to one DC power supply 10 arranged at a corner portion through seven power supply lines 8o, 8p, 8q, 8r, 8s, 8t, and 8u formed by different conductor patterns. In addition, seven bypass capacitors 19a, 19b, 19c, 19d, 19e, 19f, and 19g surface mounted and grounded are connected to the LSIs 6h, 6i, 6j, 6k, 6l, 6m, and 6n, respectively.
FIG. 12 is a side sectional view showing the basic structure of main part of the multilayered printed circuit board incorporating a high-k dielectric.
This multilayered printed circuit board incorporating a high-k dielectric has a structure in which a power supply layer that constructs a power supply line 8 is sandwiched from both sides by ground plane layers that construct ground lines 9 via high-k insulating member layers by high-k insulating members 4, and this portion is sandwiched from both sides by signal layers 20 via prepreg insulating layers 21. With this structure, a line structure having a low impedance is implemented.
In this multilayered printed circuit board incorporating a high-k dielectric as well, a high frequency power supply current generated in accordance with the high speed, high frequency operation of a high speed, high frequency circuit element or a technique for suppressing it is not disclosed. In addition, the high frequency characteristic of the decoupling inductor and bypass capacitor can be regarded as insufficient. Nevertheless, the multilayered printed circuit board incorporating a high-k dielectric can be practically employed with relative ease to avoid the influence of high frequency power supply current. As a characteristic feature, the multilayered printed circuit board incorporating a high-k dielectric has the power supply lines 8o, 8p, 8q, 8r, 8s, 8t, and 8u which do not largely depend on the types of the LSIs 6h, 6i, 6j, 6k, 6l, 6m, and 6n or utilization conditions and allow the high speed, high frequency operation of the LSIs 6h, 6i, 6j, 6k, 6l, 6m, and 6n. 
In the above described decoupling circuit or multilayered printed circuit board incorporating a high-k dielectric, which has an EMI suppressing effect, the characteristics of the bypass capacitor introduced into the decoupling circuit are problematic because improvements in the material technology and structural technology are considerably delayed as compared to the increase in speed and frequency in a high speed, high frequency circuit element such as an LSI. The high-k insulating material used in the multilayered printed circuit board incorporating a high-k dielectric must be partially used, unlike the prepreg insulating material of a normal printed circuit board mainly containing a glass epoxy resin. The current printed circuit board manufacturing process must be largely changed, and considerably long time is necessary for practice. That is, either technique cannot easily and appropriately avoid the influence of a high frequency power supply current generated in the high speed, high frequency operation mode of a high speed, high frequency circuit element.
The problem of the characteristics of the bypass capacitor will be described in detail. For example, the switching frequency of a CPU used in a recent personal computer is as high as 1 GHz or more. The power supply current of an LSI that allows such high speed switching contains a higher mode of harmonics of several GHz or more. However, the resonance frequency of a capacitor of about 0.1 μF, which is often used as a bypass capacitor in the current capacitor technology, is several ten MHz or less. In addition, inductance components due to the electrode pattern of the capacitor or lead wire are present in series in the capacitance component (the capacitor has an equivalent series inductance ESL). For these reasons, the bypass capacitor behaves as an inductor at a frequency equal to or higher than the series resonance frequency determined on the basis of the relationship to the capacitance, i.e., at a frequency more than several ten MHz, so the basic performance is lost. To allow an increase in speed of digital circuits in the future, increasing the frequency and decreasing the impedance in a wide frequency band are essential for a bypass capacitor. However, the likelihood that a high capacitance compact bypass capacitor having characteristics representing that the resonance frequency exceeds 1 GHz and a low impedance is exhibited in a wide frequency band will be developed as a practical product and become commercially available is very low.